The present invention relates to a method for improving the quality of dielectric compositions used as insulation for electrical conductor cables. More specifically, the invention relates to a method for improving the resistance to treeing of an insulting layer made from pellets comprising an organic polymeric material and an organo silane treeing inhibitor. The term "treeing" refers to a degradation of electrical insulation caused by exposure to an electric field which results in the formation of microscopic channels or tubes having a tree-like appearance. The term "water treeing" refers to slowly progressing treeing caused by the presence of moisture.
Dielectric compositions having organo silane additives for increasing resistance to treeing are disclosed in U.S. Pat. Nos. 4,144,202 and 4,212,756. To the extent not inconsistent with the present invention, the disclosures of both said patents are incorporated herein by reference.
While the organo silane additives in these patented dielectric compositions are generally successful in slowing or inhibiting growth of trees, the additives themselves are sometimes a source of undesired contamination. It is a principal objective of the present invention to provide a method for increasing resistance to treeing in a polymeric insulating layer on an electrical conductor where the insulating layer is made from a plurality of discrete pellets blended together by fusion at an elevated temperature, and some of the pellets may contain excessive levels of undesired impurities.
It is a related object of the present invention to provide a method of the type described which may be used on a continuous or mass-production scale.
The method of the present invention has the advantage of causing no detectable deterioration in pellets processed and no reduction of quality in an insulating layer made from tested pellets.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification and drawing.